The invention relates to a turbocharger for an internal combustion engine having a turbine housing with spiral inlet passages coupled to different exhaust gas lines of an exhaust train of the internal combustion engine and to an internal combustion engine, in particular a gasoline and/or diesel engine.
As a result of the continuous tightening of emission limits, such as NOx and particulate emission limits, turbochargers and supercharged engines are subject to increasingly strict requirements as well. Requirements are for example increasingly stringent with respect to boost pressure provision at high exhaust gas recirculation rates over medium to high load demand ranges of the internal combustion engine, whereby, the turbines of turbochargers are increasingly made smaller geometrically. The high turbine power output demanded of turbochargers is achieved by increasing the banking capability or reducing the absorption capability of the turbines in combination with the respective internal combustion engine. The power output of turbochargers can further be influenced by installing exhaust treatment systems such as particulate filters, catalytic converters or SCR systems into the exhaust train downstream of the turbine. These exhaust treatment system increase the pressure at an exhaust gas outlet of the turbocharger. This in turn reduces a turbine pressure gradient which characterizes the performance of the turbocharger, wherein the turbine pressure gradient can be determined as a quotient of a pressure upstream of the turbine wheel or an exhaust gas inlet of the turbine housing and a pressure downstream of the turbine wheel or an exhaust gas outlet of the turbine housing. For this reason, the size of the turbine has to be further reduced, thereby reducing its efficiency, in order to meet the power demand of the compressor of the turbocharger. Some improvement is provided by turbochargers known from prior art, the turbine housing of which comprise two independently passable spiral passages which are usually asymmetrical, and each of which is coupled to different exhaust gas lines of an exhaust train of the internal combustion engine. The exhaust gas lines themselves are assigned to different cylinders or cylinder groups of the internal combustion engine.
In the design of turbochargers, which are usually defined on the basis of the nominal operating point, the charge exchange side and the consumption side of the internal combustion engine, the lower load and speed range of internal combustion engines in particular can however not be optimized even when using turbochargers with two asymmetrical spiral passages. For this purpose, the cross-section of one spiral passage generally has to be relatively small in order to generate the required exhaust gas flow speeds. The economical sand casting process commonly used for producing the turbine housing is however subject to limits in terms of production engineering, so that only spiral passages with a width of more than 4.5 mm can be produced reliably. In addition, casting is often subject to relatively major variances of 10% or more, which leads to further efficiency losses of the turbocharger.
It is the object of the present invention to provide a turbocharger for an internal combustion engine, or an internal combustion engine fitted with a turbocharger which allows for improved efficiency in a larger operating range while involving production costs which are as low as possible.